1. Field of the Invention
This invention relates to photocrosslinkable, injectable, biodegradable oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels made from the photopolymerization of an OPF macromer with UV light and a photoinitiator. Hydrogels with varying mechanical properties and water content can be made with changes in macromer and crosslinking agent concentration in a precursor solution. The biodegradable OPF hydrogels can be injected as a fluid into a bodily defect of any shape, may incorporate various therapeutic agents, e.g., cells and/or growth factors, and may be implanted via minimally invasive arthroscopic techniques.
2. Description of the Related Art
Controlled release of bioactive molecules such as growth factors has become an important aspect of tissue engineering because it allows modulation of cellular function and tissue formation at the afflicted site. The encapsulation of drugs, proteins and other bioactive molecules within degradable materials is an effective way to control the release profile of the contained substance.
Accordingly, there is continued interest in providing injectable, photocrosslinkable and biodegradable systems for cell and drug delivery. Photopolymerizable, degradable biomaterials provide many advantages over chemically initiated thermoset systems. Photoinitiated reactions provide rapid polymerization rates at physiological temperatures. Further, because the initial materials are liquid solutions, the systems are easily placed in complex shaped volumes and subsequently reacted to form a polymer of exactly the required dimensions.
In this approach, the invasiveness of some surgical techniques is minimized as prepolymers are introduced to the desired site via injection and photocured in situ with fiber optic cables using arthroscopic techniques. (See, Anseth et al., “In situ forming degradable networks and their application in tissue engineering and drug delivery”, J Control Release, 2002; 78(1-3):199-209.) In addition, by exposing the mixture of macromer and photoinitiator to the light source, the macromer undergoes rapid crosslinking and forms a network. (See, Bryant et al., “Cytocompatibility of UV and visible light photoinitiating systems on cultured NIH/3T3 fibroblasts in vitro”, J Biomater Sci Polym Ed., 2000; 11 (5):439-57.) These networks can be used to entrap water-soluble drugs and enzymes and deliver them at a controlled rate. (See, Bryant et al., “Encapsulating chondrocytes in degrading PEG hydrogels with high modulus: engineering gel structural changes to facilitate cartilaginous tissue production”, Biotechnol Bioeng 2004 86(7):747-55; and Hatefi et al., “Biodegradable injectable in situ forming drug delivery systems” J Control. Release 2002; 80(1-3):9-28.)
One tissue engineering application that has received significant interest is the restoration of defects in cartilage. Cartilage is one of the few tissues found in the body that has limited capability to regenerate as a result of injury, congenital abnormalities or arthritis. In the past decade, many research efforts have been devoted to orthopedic tissue engineering to produce methods that restore defects in the cartilage. (See, Anseth et al., “In situ forming degradable networks and their application in tissue engineering and drug delivery”, J Control Release 2002; 78(1-3):199-209; and Bryant et al., “The effects of crosslinking density on cartilage formation in photocrosslinkable hydrogels”, Biomed Sci Instrum 1999; 35:309-14; and Burdick et al., “Delivery of osteoinductive growth factors from degradable PEG hydrogels influences osteoblast differentiation and mineralization”, J Control Release 2002; 83(1):53-63.) One of the challenges is the design and fabrication of the biodegradable scaffolds which are instructive for specific cellular functions and may thus regulate cell adhesion, proliferation, expression of a specific phenotype and extracellular matrix (ECM) deposition in a predictable and controlled fashion. (See, Genes et al., “Effect of substrate mechanics on chondrocyte adhesion to modified alginate surfaces”, Arch Biochem Biophys 2004; 422(2):161-7; and Loty et al., “Phenotypic modulation of nasal septal chondrocytes by cytoskeleton modification”, Biorheology 2000; 37(1-2):117-25; and Mahmood et al., “Adhesion-mediated signal transduction in human articular chondrocytes: the influence of biomaterial chemistry and tenascin”, C Exp Cell Res 2004; 301 (2):179-88.) It is known that cell behavior on synthetic polymers is related to both the physical and chemical properties of the substrate. (See, Mahmood et al., “Adhesion-mediated signal transduction in human articular chondrocytes: the influence of biomaterial chemistry and tenascin”, C Exp Cell Res 2004; 301 (2): 179-88; and Dadsetan et al., “Cell behavior on laser surface-modified polyethylene terephthalate in vitro”, J Biomed Mater Res 2001; 57(2):183-9; and Dadsetan et al., “Surface chemistry mediates adhesive structure, cytoskeletal organization, and fusion of macrophages”, J Biomed Mater Res 2004; 71A(3):439-48.) Scaffold physical properties may control cell function by regulating the diffusion of nutrients, waste products and cell-cell interactions, whereas scaffold surface chemistry affects cell adhesion, morphology and subsequent cellular activity by controlling protein adsorption. (See, Collier et al., “Protein adsorption on chemically modified surfaces”, Biomed Sci Instrum 1997; 33:178-83; and Jones et al., “Macrophage behavior on surface-modified polyurethanes”, J Biomater Sci Polym Ed 2004; 15(5):567-84.)
Cartilage cells are an ideal model for the study of cell-substrate interactions due to the tight relationships that have been established between chondrocytes morphology and function. (See, Miot et al., “Effects of scaffold composition and architecture on human nasal chondrocyte redifferentiation and cartilaginous matrix deposition”, Biomaterials 2005; 26(15):2479-89.) This ability arises largely from the cartilage ECM, an abundant network of collagen, protoglycan and other molecules. The ECM interacts with chondrocytes through a variety of receptors to modulate chondrocyte metabolism phenotype and response to mechanical load. (See, Genes et al., “Effect of substrate mechanics on chondrocyte adhesion to modified alginate surfaces”, Arch Biochem Biophys 2004; 422(2):161-7; and Sah et al., “Biosynthetic response of cartilage explants to dynamic compression”, J Orthop Res 1989; 7(5):619-36.) Understanding how chondrocytes respond to specific, individual ECM signals would provide insights into the pathogenesis of diseases like osteoarthritis, which is known to be precipitated by mechanical factors. (See, Radin et al., “Effects of mechanical loading on the tissues of the rabbit knee”, J Orthop Res 1984; 2(3):221-34; and Cooper et al., “Occupational activity and osteoarthritis of the knee”, Ann Rheum Dis 1994; 53(2):90-3.)
In vitro chondrocyte culture on substrates in two dimensions has been shown to reduce gene expression and production of cartilage specific proteins such as collagen type II and aggrecan and quickly dedifferentiate to a more fibroblastic phenotype. (See, Loeser, “Integrin-mediated attachment of articular chondrocytes to extracellular matrix proteins”, Arthritis Rheum 1993; 36(8):1103-10.) A number of researches have investigated techniques to reexpress the chondrogenic phenotype during chondrocyte expansion in monolayer culture by growing cells on microcarriers using growth factors, such as basic fibroblastic growth factors (bFGF-2) (See, Martin et al., “Enhanced cartilage tissue engineering by sequential exposure of chondrocytes to FGF-2 during 2D expansion and BMP-2 during 3D cultivation”, J Cell Biochem 2001; 83(1):121-8), or incorporating cytoskeleton modifying drugs such as cytochalasin D. (See, Loty et al., “Cytochalasin D induces changes in cell shape and promotes in vitro chondrogenesis: a morphological study”, Biol Cell 1995; 83(2-3):149-61.) However, the impact of material properties on the events that regulate cellular phenotype has not been extensively researched. (See, Mahmood et al., “Adhesion-mediated signal transduction in human articular chondrocytes: the influence of biomaterial chemistry and tenascin”, C Exp Cell Res 2004; 301(2):179-88; and Papadaki et al., “The different behaviors of skeletal muscle cells and chondrocytes on PEGT/PBT block copolymers are related to the surface properties of the substrate”, J Biomed Mater Res 2001; 54(1):47-58.)
A variety of materials have been suggested for the use in cartilage repairs. These materials have included natural polymers such as collagen, alginate and hyaluronic acid as well as synthetic polymers such as polyacrylamides, poly(vinyl alcohol) and poly(ethylene glycol) (PEG). (See, Yaylaoglu et al., “Development of a calcium phosphate-gelatin composite as a bone substitute and its use in drug release”, Biomaterials 1999; 20(8):711-9; and Rowley et al., “Alginate hydrogels as synthetic extracellular matrix materials”, Biomaterials 1999; 20(1):45-53; and Temenoff et al., “Injectable biodegradable materials for orthopedic tissue engineering”, Biomaterials 2000; 21(23):2405-12; and Jasionowski et al., “Thermally-reversible gel for 3-D cell culture of chondrocytes”, J Mater Sci Mater Med 2004; 15(5):575-82; and Noguchi et al., “Poly(vinyl alcohol) hydrogel as an artificial articular cartilage: evaluation of biocompatibility”, J Appl Biomater 1991; 2(2):101-7; and Cruise et al., “In vitro and in vivo performance of porcine islets encapsulated in interfacially photopolymerized poly(ethylene glycol) diacrylate membranes”, Cell Transplant 1999; 8(3):293-306; and Wallace et al., “A tissue sealant based on reactive multifunctional polyethylene glycol”, J Biomed Mater Res 2001; 58(5):545-55.)
Oligo (poly (ethylene glycol) fumarate) (OPF) is a macromer that has been developed and has been used for fabrication of hydrogels with a redox initiation system. It is reported that OPF hydrogels are biodegradable and their mechanical properties and degradation rates are controlled by the molecular weight of the PEG used in macromer formation. (See, Jo et al., “Modification of oligo(poly(ethylene glycol) fumarate) macromer with a GRGD peptide for the preparation of functionalized polymer networks”, Biomacromolecules 2001; 2(1):255-61; and Temenoff et al., “Effect of poly(ethylene glycol) molecular weight on tensile and swelling properties of oligo(poly(ethylene glycol) fumarate) hydrogels for cartilage tissue engineering”, J Biomed Mater Res 2002; 59(3):429-37; and U.S. Pat. No. 6,884,778; and U.S. Patent Application Publication No. 2002/0028189.)
Thus, there is still a need for photocrosslinkable, injectable, biodegradable hydrogels that can be injected as a fluid into a bodily defect and photocrosslinked in the defect, that may incorporate various therapeutic agents, e.g., cells and/or growth factors, and that may be implanted via minimally invasive arthroscopic techniques.